Scanned laser vein contrast enhancer using a single laser

ABSTRACT

The present invention is a Miniature Vein Enhancer that includes a Miniature Projection Head. The Miniature Projection Head may be operated in one of three modes, AFM, DBM, and RTM. The Miniature Projection Head of the present invention projects an image of the veins of a patient, which aids the practitioner in pinpointing a vein for an intravenous drip, blood test, and the like. The Miniature projection head may have a cavity for a power source or it may have a power source located in a body portion of the Miniature Vein Enhancer. The Miniature Vein Enhancer may be attached to one of several improved needle protectors, or the Miniature Vein Enhancer may be attached to a body similar to a flashlight for hand held use. The Miniature Vein Enhancer of the present invention may also be attached to a magnifying glass, a flat panel display, and the like.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/700,729, filed Jan. 31, 2007, which is a continuation in part ofapplication Ser. No. 11/478,322, filed on Jun. 29, 2006 and also claimspriority on provisional patent application entitled Three DimensionImaging of Veins, application Ser. No. 60/817,623, also filed on Jun.29, 2006, all disclosures of which are hereby incorporated by reference.

FIELD OF INVENTION

The invention described herein relates generally to an imaging device,in particular, an imaging means for enhancing visualization ofcomponents covered by living tissue thin opaque films. Moreparticularly, the present invention is directed to enhancing thevisualization of veins, arteries and other subcutaneous structures ofthe body for inter alia facilitating fluid insertion into or extractionfrom the body or otherwise visualizing subcutaneous structures fordiagnosis of the medical condition of a patient or administration ofmedical treatment to a patient.

BACKGROUND OF THE INVENTION

A visit to a doctor's office, a clinic or a hospital may necessitatevascular access that is, the insertion of a needle or catheter into apatient's vein or artery. These procedures may be required for manyreasons including: to administer fluids, drugs or solutions, to obtainand monitor vital signs, to place long-term access devices, and toperform simple venipunctures. Vascular access ranks as the most commonlyperformed invasive medical procedure in the U.S—over 1.4 billionprocedures annually—as well as the top patient complaint among clinicalprocedures. The overwhelming majority of vascular access procedures isperformed without the aid of any visualization device and relies on whatis observed through the patient's skin and by the clinician's ability tofeel the vessel—basically educated guesswork.

Medical literature reports the following statistics: 28% first attemptIV failure rate in normal adults, 44% first attempt IV failure inpediatrics, 43% of pediatric IVs require three or more insertionattempts, 23% to 28% incidence of extravasations/infiltration, 12%outright failure rate in cancer patients, 25% of hospital in-patientsbeyond three days encounter difficult access. The miniature veinenhancer of the present invention may be used by a practitioner tolocate a vein and is particularly useful when trying to locate a vein inthe very old, very young or obese patients. More than fifty percent ofattempts to find a vein in the elderly, who have a generally highpercentage of loose, fatty tissue, and in children, who have a generallyhigh percentage of small veins and “puppy fat”, are unsuccessful. Thepresent invention is aimed at reducing and/or preventing the discomfortand delay associated with botched attempts to pierce veins forinjections and blood tests. In addition, the present invention can cutthe time it takes to set up potentially life-saving intravenous drip.During venous penetration, whether for an injection or drip, it isessential to stick a vein in exactly the right location. If apractitioner is only slightly off center, the needle will more thanlikely just roll off and require a re-stick.

Other Approaches

It is known in the art to use an apparatus to enhance the visualappearance of the veins in a patient to facilitate insertion of needlesinto the veins. An example of such a system is described in U.S. Pat.Nos. 5,969,754 and 6,556,858 incorporated herein by reference as well asa publication entitled “The Clinical Evaluation of Vein ContrastEnhancement”. Luminetx is currently marketing such a device under thename “Veinviewer Imaging System.”

The Luminetx Vein Contrast Enhancer (hereinafter referred to as LVCE)utilizes an infrared light source (generated by an array of LEDs) forflooding the region to be enhanced with infrared light. A CCD imager isthen used to capture an image of the infrared light reflected off thepatient. The resulting captured image is then projected by a visiblelight projector onto the patient in a position closely aligned with theimage capture system. Given that the CCD imager and the image projectorare both two dimensional, and do not occupy the same point in space, itis relatively difficult to design and build a system that closely alignsthe captured image and the projected image.

A further characteristic of the LVCE is that both the imaging CCD andthe projector have fixed focal lengths. Accordingly, the patient must beat a relatively fixed distance relative to the LVCE. This necessitatesthat the LVCE be positioned at a fixed distance from the region of thepatient to be enhanced.

The combination of the size of the LVCE and the fixed focal arrangementprecludes using the LVCE as small portable units that are hand held.

Other patents such as U.S. Pat. No. 6,230,046, issued to Crane et al.,implement a light source for illuminating or trans-illuminating thecorresponding portion of the body with light of selected wavelengths anda low-level light detector such as an image intensifier tube (includingnight vision goggles), a photomultiplier tube, photodiode or chargecoupled device, for generating an image of the illuminated body portion,and optical filter(s) of selected spectral transmittance which can belocated at the light source(s), detector, or both.

All cited references are incorporated herein by reference in theirentireties. Citation of any reference is not an admission regarding anydetermination as to its availability as prior art to the claimedinvention.

OBJECTS OF THE INVENTION

The present invention is directed to technologies and processesassociated with the use of one or more moving laser light sources todetect the presence of blood-filled structures, such as venous orarterial structures, below the surface of the skin and to project animage back on to the skin that shows the operator the pattern ofdetected structures. The present approach uses one or more laser lightsources that are scanned over the body using mirrors and a lightdetector that measures the reflections of the laser light and uses thepattern of reflections to identify the targeted blood rich structures.Various preferred approaches are described for the main subsystems ofthe design as well as various alternative techniques for accomplishingthe objects of this invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows an embodiment of the present invention that uses twomirrors to generate a raster pattern of light, with each mirror mountedusing a single degree of freedom, and where a beam of light that strikesthe first moving mirror is then reflected towards the second movingmirror.

FIG. 1B and FIG. 1C each show a respective waveform representative ofthe frequency at which each mirror in the embodiment of FIG. 1A iscaused to oscillate about the corresponding fulcrum, to generate theraster pattern.

FIG. 1D shows the resulting raster pattern generated by the embodimentof FIG. 1A.

FIG. 1E shows an embodiment of the present invention that uses a singlemirror to generate a Lissajous pattern of light, with the single mirrorbeing mounted to move on two axes created by two fulcrum pairs.

FIG. 1F and FIG. 1G each show a respective waveform representative ofthe frequency at which the mirror in the embodiment of FIG. 1E is causedto oscillate about the corresponding fulcrum, to generate the Lissajouspattern.

FIG. 1H shows the resulting Lissajous pattern generated by theembodiment of FIG. 1E.

FIG. 1I shows an embodiment of the present invention that uses a singlemirror moving about two axes in order to generate a collapsing ellipsepattern of light.

FIG. 1J and FIG. 1K each show a respective waveform representative ofthe frequency at which the mirror in the embodiment of FIG. 1I is causedto oscillate about the corresponding fulcrum, to produce the collapsingellipse pattern.

FIG. 1L shows the collapsing ellipse pattern generated by the embodimentof FIG. 1I.

FIG. 1M shows an embodiment of the present invention that uses a singlemirror moving about two axes in order to generate a spiral pattern oflight.

FIG. 1N and FIG. 1P each show a respective waveform representative ofthe frequency at which the mirror in the embodiment of FIG. 1M is causedto oscillate about the corresponding fulcrum, to generate the spiralpattern.

FIG. 1Q shows the resulting spiral pattern generated by the embodimentof FIG. 1M.

FIG. 2A shows a first mirror system for folding and scanning the laser'slight, and includes a laser source oriented to emit light toward amirror placed in the path of the laser light at an angle to the lightbeam that is calculated to bounce the light beam into a new desireddirection.

FIG. 2B shows a laser source oriented to emit a beam of light thatstrikes a mirror at the appropriate angle and position, with the mirrormoving on a single axis to project a single line on the target surface.

FIG. 2C shows a laser beam emitted by a laser source, with the beambeing projected to strike a mirror at a desired position and angle, withthe mirror being oriented to reflect the beam to strike the appropriateposition on a second mirror that may move about a single axis.

FIG. 2D shows a laser beam emitted by a laser source, with the beambeing projected to strike a first moving mirror at a desired positionand angle, with the mirror moving about one axis to reflect the beam tostrike a second moving mirror that may similarly move about a singleaxis, with the light being reflected off of the second mirror to form atwo dimensionally shaped scanning pattern on the target area.

FIG. 3 shows the use of a dielectric mirror to combine multiple lasersinto a coaxial output beam

FIG. 4 shows the use of a polarized mirror to combine multiple lasersinto a coaxial output beam

FIG. 5A shows the use of an array of lasers to eliminate the need for asecond moving mirror for scanning the laser light.

FIG. 5B shows a side view of the array of lasers of FIG. 5A.

FIG. 6 shows the use of a light valve element to eliminate the need fora second moving mirror for scanning the lasers

FIG. 7A shows a system for detecting a vein and re-projecting an imagealong the same path.

FIG. 7B provides a representation of the signal amplitude of the laseroutput used by the system of FIG. 7A.

FIG. 7C illustrates a representation of the signal amplitude of theinput received by the photo detector of the system of FIG. 7A.

FIG. 7D provides a representation of the signal amplitude for thecorrected signal that would be seen in the later stages of the detectioncircuitry of the system of FIG. 7A.

FIG. 7E provides a representation of the signal amplitude for the outputsignal from the detection circuitry, as used by the system of FIG. 7A,indicating detection of a vein.

FIG. 8A shows a single laser pulse width modulation scheme in which themodulation of the laser between detection and projection is in realtime.

FIG. 8B shows an embodiment where the laser output signal waveform hastwo levels, bright and dim, where for a single laser system, the brightsignal may be used to project and the dim signal may be used to scan.

FIG. 8C illustrates an embodiment with two lasers, where the first laserand the second laser are each amplitude modulated at differentfrequencies to cause the reflected light received at the photo detectorto also be frequency modulated.

FIG. 8D shows a waveform representative of the amplitude modulatedfrequency at which the first laser of the embodiment in FIG. 8C ismodulated.

FIG. 8E shows a waveform representative of the amplitude modulatedfrequency at which the second laser of the embodiment in FIG. 8C ismodulated.

FIG. 9 shows a focusing system for an LED.

FIG. 10A shows a mechanical focusing device for an LED embodiment of theinvention, where the mechanical device includes an open base.

FIG. 10B shows another mechanical device for an LED embodiment, wherethe device is a rod extending from the scan head and having theappropriate length, so that the distance is maintained when the end ofthe rod touches the skin.

FIG. 11 shows an auto-focus system for a camera/projector basedembodiment of the invention.

FIG. 12 shows the waveform of the reflected signal.

FIG. 13 shows an array of photo detectors arrange to increase thedetection area in proportion to the angle from center.

FIG. 14 shows the use of a short wavelength laser in combination with aninfrared laser to eliminate the effect of the changing topology of thebody as the laser scans across its surface.

FIG. 15 shows a vein lock system that aids in the discrimination ofveins from other structures.

FIG. 16 shows the preferred wavelengths for various elements in thesystem.

FIG. 17 shows a side view of a prototype embodiment of the invention.

FIG. 18 shows an alternate side view of a prototype embodiment of theinvention.

FIG. 19A shows a subassembly of a prototype embodiment of the invention.

FIG. 19B shows a perspective view of the holder assembly shown in FIG.19A.

FIG. 19C shows a second perspective view of holder assembly of FIG. 19B.

FIG. 20 shows a view of the prototype embodiment with parts removed sothat the laser path and the key components controlling the laser pathare visible.

FIG. 21 shows an alternative view of the prototype embodiment with partsremoved so that the laser path and the key components controlling thelaser path are visible.

FIG. 22 shows a view of the prototype embodiment with a circuit boardremoved so that additional elements are visible.

FIG. 23 shows a prototype embodiment from a top-side view.

FIG. 24 shows the prototype embodiment of FIG. 23, but with the scanhead separated from the handle.

FIG. 25 shows a side view of the prototype embodiment of FIG. 23.

FIG. 26 shows a bottom view of the prototype embodiment of FIG. 23.

FIG. 27A shows the prototype embodiment of FIG. 23 with the housing ofthe head and handle removed, so that the internal assembly is visible.

FIG. 27B shows the housing that was removed from the prototypeembodiment of FIG. 27A.

FIG. 28 shows the top part of the enclosure of a prototype embodimentwith the other parts removed.

FIG. 29 shows a block diagram of a prototype embodiment of theinvention.

FIG. 30 shows a Fresnel lens assembly that can be used to enhance thereturn signal from the edges of the scan area.

SUMMARY OF THE INVENTION Using One or More Lasers to Capture and Projectan Image

Blood vessels, both venous and arterial, absorb red, near infrared andinfrared (IR) light to a greater degree than surrounding tissues absorbthose wavelengths of light. Therefore when illuminating the surface ofthe body with infrared light, blood rich tissues such as veins willabsorb more of this light and other tissues will reflect more of thislight. Analysis of this pattern of reflections enables the veins to belocated. The present invention includes both a positive or negativeimage that is projected in the presence of a vein. Thus, a vein can berepresented by a bright area and the absence of a vein can be presentedas a dark area and vice versa.

A laser diode is preferred in the present invention as it emits lightover a known, narrow wavelength range and when appropriately focusedprojects a small spot that varies very little in size over a wide rangeof distances. This is an effect that is commonly seen in laser pointersand laser gun sights.

-   -   1. In addition to a laser diode, the laser light used in the        present invention can be generated by other laser light emitting        elements including but not limited to VCSEL lasers, other        semiconductor lasers and other solid state lasers. In the        present invention a narrow wavelength of light is emitted        producing a constant spot size even when the range to the target        varies. The narrow wavelength allows a laser diode or diodes to        be selected that have the desired characteristics of the ability        to detect blood through differential absorption and the ability        for a human eye to detect the reflected light. As will be        discussed, certain embodiments may require differing tradeoffs        in light wavelength. Additionally, the same characteristics of        the laser that make it beneficial for detecting blood presence        with useful resolution also makes it useful for projecting the        pattern of blood and vein distribution back on to the skin. The        major difference is laser selection for the projection        application is to ensure that the wavelength of the light is        within the visible spectrum for the human eye. For example, 635        nm light is perceived as bright red light by the human eye,        while an IR laser at 740 nm is nearly invisible to the eye but        is absorbed more by blood vessels than by surrounding tissues        and can be measured using various photo detector technologies.        Other colors of light such as green have significant benefits as        the projected color since the eye is most sensitive to these        wavelengths and it has a high contrast with many skin colors.        Furthermore, in certain embodiments a single color laser may be        selected that through novel techniques can perform both the        projector and scanner functions. In this application, terms        visible and infrared light are used to describe approximate        wavelengths of light being used in the invention. Furthermore,        specific wavelengths have been referenced in certain        embodiments. These conventions were used for both clarity of        discussion and as specific references to devices and wavelengths        that are commercially available today. Referring to FIG. 16, the        useful spectrum for each of the critical functions in a        detection system is shown. As new devices become commercially        available with desirable characteristics they can be used in the        invention as long as their wavelengths fall in or near the        identified ranges for their particular function. For example, a        785 nm laser might be a preferred embodiment since it would be:        -   a. Lower cost since it is produced in high volumes for use            in DVD players        -   b. Available in higher power versions of 120 milliwatts and            above        -   c. Easier to separate from 638 nm since their wavelengths            are further from each other        -   d. Less divergent

Additionally, the use of laser as opposed to other techniques known inthe art such as the Luminetx product allows finer control over thescanning for blood vessels. Since the laser is only striking a singlespot on the body, the laser that is used to detect the presence of bloodcan be modulated on the fly wherein the intensity can be increased ordecreased on a spot by spot basis. In a camera based solution, since theinfrared light floods the area being scanned, no such control ispossible.

Mirrors

Through the use of movable mirrors, the laser spot can be rapidly movedacross the target area of the body. As the spot moves across the bodythere will be a modulation of the amplitude of the reflected light thatis proportional to the attributes of that point on the body. Forexample, red, near IR and IR light will be absorbed and reflected inproportion to the amount of blood at the point at which the laserstrikes the body. The invention uses this modulation to determine thelocation of veins. Other wavelengths of light will be reflected inproportion to the topology of the body at the point at which the laserstrikes and can be used for enhancing vein detection.

Scan Mirrors

The invention uses one or more moving mirrors to move the laser lightspot across the patient's skin in a variety of different possiblepatterns. The laser light is projected from a light generator on to themirror and as the mirror is moved, the projected spot of light moves asa function of the angle of the mirrors at a given moment in time. Thelight is projected on to one or more mirrors moving in a coordinated wayso as to generate a pattern of light on the target surface such as thepatient's skin. Many patterns are possible by changing mirror attributessuch as mirror size, position in relationship to each other and to thelaser or lasers, the degree of the mirror's angle and the speed ofmirror movement.

Random Vs. Fixed Patterns

A scanning method implemented with the present invention is unique inits approach to scanning the target area. In general, the lower thelevel of precision required in positioning the laser spot, the easierand less costly it is to produce the pattern.

Coaxial Lasers

In a preferred embodiment, instead of a laser projector there is no needfor a reproducible scan pattern so that from frame to frame the laserscan lines do not need to fall reproducibly upon the scan lines of theprior frame, thus, there is no need to know the instantaneous positionof the laser. The reason being, the light used for detection and forprojection are either from the same light source or from multiplecoaxially aligned light sources and the vein detection is performed innear real time. The projected visible light can be modulated in realtime so that whatever location is being imaged is instantaneously beingprojected and only a small offset between detection and projectionoccurs which will not be noticeable to the user. Therefore, since theimage projection happens within the scan, it doesn't matter if the scanpattern on the next traversal of the area proceeds in the same way theprevious scan pattern did.

Parallel Lagging Projection Laser

If small additional processing time is required, rather than coaxiallyarranging the scan and projection lasers, the system can hold themparallel with a small gap in one direction. In this way, the spotsfollow closely behind each other as the mirrors move, but there isadditional time between when the detection spot hits a point on the bodyand when the closely following projection, spot hits the body.

Repeatable Patterns

In other embodiments, there are benefits to knowing the instantaneousposition of the laser spot. In such embodiments, the desire would be todelay the projection of the image so that analysis that requiresadditional time can be performed.

A raster pattern is one type of repeatable pattern. In such a pattern,there are a number of different delay strategies.

-   -   1. A short time delay that is a subset of a scan line where the        lasers are arranged in parallel rather than coaxially so that        the projection spot lags slightly behind the detection spot.    -   2. Alternating scan lines where as the lasers pass right to left        the system performs detection and as it passes from left to        right it projects    -   3. Alternating frames where the lasers complete their full x and        y travels while capturing the information into memory and then        projecting on the subsequent frame.

These differing approaches each have benefits. The shorter the timedelay between capture and projection, the less complicated the systemneeds to be in terms of processing and memory. As the delay increases,more information needs to be stored and processed, and hand jitterbecomes more of an issue. If the frame rate is fast enough, the userwould not notice the lag even with the occurrence of hand jitter. Handjitter is the result of motion of the hand holding the scanner inrelationship to the body. In typical systems with frame rates of 30-60Hz one or two frame delay is practical. If additional frames are neededfor processing, than the frame rate can be increased to minimize thedelay. Alternatively, the system can use digital or optical imagestabilization well known in the art to maintain alignment from frame toframe. One method would be to use accelerometers can be used todetermine the amplitude and direction of the movement from frame toframe. Many other techniques are well known in the art.

The positive side of frame-level or multi-frame delay is that morecomplex algorithms can be used to identify the veins such as edgedetection and line detection algorithms that are well know in the art.

Averaging Across Frames

One embodiment of a system that uses repeatable scanning is one in whichthe image is averaged across two or more frames, thereby increasing thequality of the image captured and therefore increases the ability of thesystem to accurately detect the position of blood vessels.

Pattern Generation

Many patterns of scanning are possible. For example, the patterns can bebased on raster, collapsing ellipse, spirals, lissajous or random.Tradeoffs between pattern and system complexity can be made to createmultiple products of differing cost and performance. For example, if themirrors are run at their natural resonance frequency, the systemminimizes the power needed to move the mirrors thereby either extendingbattery life or reducing the battery size needed and thereby reducingsize, weight and cost.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 a-1 d, preferred embodiments are shown that generateraster, lissajous and collapsing ellipse and spiral patterns. Thedrawings show the mirror (e.g., 1250) on top of the electrical wave form(e.g., 1258) that is applied to the mirror to control its motion. Thesesinusoidal wave forms move the mirror in a back and forth pattern withmaximum deflection at the peak of the wave, rest at the center of thewave and the opposite maximum deflection at the opposite peak of thewave. Also indicated in the drawing are the most preferred frequenciesand the preferred ranges that would be used in an implementation of theinvention.

Raster Pattern Generation

In FIG. 1 a, a raster pattern 1257 is generated using two mirrors.Mirror 1250 is mounted so that it has a single degree of freedom ofmotion at fulcrum 1251/1252. A laser light source as described elsewherestrikes the mirror at an appropriate angle so that the angle ofreflection is such that the light properly strikes the second mirror1255. Mirror 1250 oscillates at a high frequency, for example, such as20 KHz 1258. This generates the horizontal motion in the raster pattern1257. The now moving beam 1253 is projected on to the second mirror 1255so that it is parallel to its axis of movement. Mirror 1255 is mountedso that it has a single degree of freedom of motion at fulcrum1254/1256. Mirror 1255 moves at a slower rate such as, for example, 60Hz as shown in waveform 1259. The generated pattern is bi-directional,with the beam moving right to left and left to right as the fast mirror1250 moves and top to bottom and bottom to top as the slow mirror 1255moves.

A preferred embodiment uses 20 KHz for waveform 1258 and 60 Hz forwaveform 1259. Other preferred embodiments can use 7 KHz to 35 KHz forwaveform 1258 and 45 Hz to 90 Hz for waveform 1259.

Lissajous Pattern Generation

Referring to FIG. 1E, a preferred embodiment for the generation of alissajous pattern 1265 using a single mirror 1272 that can move on twoaxes is shown. An alternative embodiment would be to use two mirrorsarranged as shown in FIG. 1 a but modulated as described for thelissajous pattern. The mirror is capable of moving along the axescreated by fulcrum pairs 1266/1269 and 1267/1268. The mirrors are movedat different frequencies and in a specific phase relationship togenerate this pattern. A lissajous pattern is mathematically describedby the equations:X=A sin(at+phase), Y=B sin(bt)The two axes are modulated based on this relationship where variousvalues of A, B and the phase offset control the specifics and density ofthe projected lissajous pattern. Waveform 1270 shows the X value overtime and waveform 1271 shows the Y value over time. In the equation, Ais the amplitude of waveform 1270 and B is the amplitude of waveform1271. at and bt are the angle of the sine waves over time and phase isthe phase shift (angle offset) between the two waveforms 1270/1271. Manyvalues of these variables can be used for a scanning application, but apreferred embodiment would select values that move the mirror at itsresonant frequencies so as to minimize power consumption.

A preferred embodiment uses 400 Hz for waveform 1270 and 60 Hz forwaveform 1271. Other preferred embodiments can use 300 KHz to 35 KHz forwaveform 1270 and 45 Hz to 90 Hz for waveform 1271.

Collapsing Ellipse Pattern Generation

In FIG. 1I, the system is configured for a collapsing ellipse pattern1286 where a series of loops are drawn across the target area with eachcircle either slightly smaller or slightly larger than the previouslydrawn circle. Again, a single mirror 1287 is shown, but the samefunction can be performed with two moving mirrors. The mirror is capableof moving along the axes created by fulcrum pairs 1282/1284 and1285/1283. The mirrors are moved at identical frequencies and are 90degrees out of phase to generate this pattern. The X direction of mirrormovement is controlled by the waveform 1280. The Y direction of mirrormovement is controlled by the waveform 1281. This waveform 1281 isamplitude modulated so that each subsequent full wave is slightlychanged in amplitude so that a different sized circle is drawn.

A preferred embodiment uses 8 KHz for waveform 1280 and 8 KHz forwaveform 1281. Other preferred embodiments can use 7 KHz to 35 KHz forwaveform 1280 and 7 KHz to 35 KHz for waveform 1281.

Spiral Pattern Generation

The spiral pattern 1290 in FIG. 1M is shown generated by a single mirror1297 but could be drawn with two mirrors as previously shown. The mirroris capable of moving along the axes created by fulcrum pairs 1291/1293and 1292/1294. The mirrors are moved at identical frequencies and are 90degrees out of phase to generate this pattern. The X direction of mirrormovement is controlled by the waveform 1295. The Y direction of mirrormovement is controlled by the waveform 1296. Both waveforms 1295/1296are amplitude modulated in a sawtooth pattern generating a spiralpattern.

A preferred embodiment uses 8 KHz for waveform 1295 and 8 KHz forwaveform 1296. Other preferred embodiments can use 7 KHz to 35 KHz forwaveform 1295 and 7 KHz to 35 KHz for waveform 1296.

Bounce Mirrors

In addition to moving mirrors, one or more fixed mirrors may be used inthe design of the invention. This allows many different arrangements ofthe light sources to minimize overall size or to otherwise optimize thepositioning of the components of the device.

Referring to FIG. 2 a, the laser source 10 is oriented to emit light 13in a desired direction. A mirror 11 is placed in the path of the laserlight at an angle to the light beam that is calculated to bounce thelight beam 14 into the new desired direction. Additional mirrors 12 canbe placed in the path of the beam to further redirect the light beam 15into a desired orientation. Although two mirrors are shown in FIG. 2 a,as many or as few mirrors as required can be used. Additionally,although FIG. 2 a is drawn in two dimensions and the angles shown areright angles; these angles can be set so that the beam is reoriented atany angle required in three dimensions.

In FIG. 2 b, the laser source 20 is oriented so that the beam 21 strikesthe mirror 22 at the appropriate angle and position. Mirror 22 is amoving mirror with an axis of motion shown at 24. In FIG. 2 b, themirror is presented as moving on a single axis and therefore projects asingle line on the target surface. Mirrors with two degrees of freedomare well known in the art and mirror 22 can be replaced by such a mirrorso that it projects a two dimensional scan and projection field on thetarget area. Alternatively, a second moving mirror can be used as willbe described in FIG. 2 d.

Note that the laser beam 21 can be redirected by one or more bouncemirrors as shown in FIG. 2 b if necessary to the specific embodiment.Such an implementation is shown in FIG. 2 c. Laser source 30 projects abeam of light 31 so as to strike the mirror at the desired position andangle. Mirror 32 is oriented so that the reflected beam 33 strikes theappropriate position on the moving mirror 34. Again, the for ease ofdrawing, mirror 34 is shown moving on a single axis 35, but can bereplaced by a mirror with two degrees of freedom so as to project andscan a two dimensional area with only a single mirror.

FIG. 2 d shows a two mirror system that is used to project and image atwo dimensional area. The laser source 50 is oriented so that the beam51 strikes the mirror 52 at the appropriate angle and position.Intermediate bounce mirrors could be placed in the beam path 51 toreorient the beam. Mirror 52 is a moving mirror with an axis of motionshown at 53. The now moving beam of light 54 is directed to movingmirror 55. Mirror 55 has an axis of motion 56 that is oriented at anangle such as 90 degrees from the axis of motion of mirror 52 shown at53. In this manner, the light reflected off of mirror 56 forms a twodimensionally shaped scanning pattern 59 on the target area 58.

Different embodiments will use one or more laser colors and sources toperform detection and projection. One embodiment of the invention usestwo lasers to perform its functions where one laser is selected to haveoptimum performance at blood detection (e.g., 740 nm) and the secondlaser has optimum characteristics to project the resulting image to theuser (e.g., 638 nm). The major benefits of this embodiment include theability to modulate the detection and visible lasers simultaneously, andthe ability to select lasers that have ideal characteristics for thefunction to be performed (rather than a trade off between detection andvisibility as will be seen in a single laser embodiment). The lasersources (e.g., FIG. 2 d, 10), can be an assembly that provides one ormore colors of laser light either arranged either coaxially side by sidein parallel.

Combining Lasers with Polarization or Dielectric Mirror

A key element of this embodiment is a mirror system that in addition tomoving the light spot as previously described provides a mechanism thatcauses the two laser beams to become coaxial so that both lasers strikethe same point on the patients skin. There are many different ways toalign co-axially the visible laser and the infrared laser including theuse of dielectric mirrors.

Combining Lasers with Dielectric Mirrors

Dielectric mirrors are specially coated mirrors that can reflectselected wavelengths (or wavelength ranges) of light while allowingother wavelengths to pass through the mirror. In this embodiment one ormore coated mirrors are used in the optical path to make the separatelaser sources coaxial so that when they strike the moving mirrorsubsystem, they then strike the same spot on the skin.

Furthermore, separate control systems are provided to modulate theintensities of the lasers. The laser intensities can be independentlymodulated to control the desired characteristics such as depth ofdetection and the brightness of the projected image providing a greatdegree of control over these desirable characteristics.

Additional embodiments are possible where additional lasers are added toprovide for further refinement of the detection and presentation of thedetected blood. For example an additional laser could be used todetermine range to the surface of the skin so that finer control overthe depth of detection can be performed. Another example is the use of asecond color of visible light so that additional information aboutuseful attributes such as depth of the blood vessel can be presented tothe user.

FIG. 3 depicts a dielectric mirror approach. The mirror is shown withthe infrared laser placed behind the dielectric mirror. The dielectricmirror is selected so that the infrared laser (e.g., 740 nm) passesthrough the mirror. The back side of the mirror can be coated with ananti-reflective coating 106 to minimize loss of intensity of theinfrared light due to reflection from the back surface of the mirror. Italso minimizes the shielding necessary for the back reflection of theinfrared light. Note that there is a refraction effect on the infraredlaser that is adjusted for by the proper alignment of the lasers. Thevisible laser (e.g., 638 nm) is directed to the front surface of themirror which is coated with a material that reflects the light of thatlaser. The combination of the transmitted laser light and the reflectedlaser light is now aligned and exits the assembly coaxially. Variousimplementations can be created that alternate the positions of thevisible and infrared lasers.

Similar assemblies can be repeated multiple times for creating coaxialcombinations of more than two lasers if needed for the specificmarketing or technical requirements of the product.

Combining Lasers with Polarized Elements

A characteristic of laser light is that it is polarized in a knownorientation. By carefully controlling the orientation of the laserlight, dielectric elements that reflect and pass light polarized inspecific orientations can be used to coaxially align the lasers.

With regard to the polarized approach, referring to FIG. 3 and replacingthe dielectric coated mirror with a polarized element as shown in FIG.4. One laser is polarized in a first orientation and is placed behindthe polarized element. The polarized element is selected so that thefirst polarized orientation passes through but the second polarizedangle is reflected. The second laser is polarized to the secondpolarized angle and is aimed at the front of the polarized element andis angled and aimed so that the reflection of the first laser is coaxialwith the second laser passing through the polarized element.

In FIG. 4, the element 110 is shown with the infrared laser 111 placedbehind the polarizing element. The laser 111 polarization (orientation)and the polarizer 113 orientation is selected so that the infrared laser111 passes through the element. The back side of the element can becoated with an anti-reflective coating 116 to minimize loss of intensityof the infrared light due to reflection from the back surface of theelement. It also minimizes the shielding necessary for the backreflection of the infrared light. Note that there is a refraction effecton the infrared laser 115 that is adjusted for by the proper alignmentof the lasers. The visible laser 112 is directed to the front surface ofthe element 113 polarized so that it is reflected by the element. Thecombination of the transmitted laser light and the reflected laser lightis now aligned and exits the assembly coaxially. While element 110 showsa coating on the front surface, the coating may also be placed on theopposite surface.

Similar assemblies can be repeated multiple times for creating coaxialcombinations of more than two lasers if needed for the specificmarketing or technical requirements of the product. Additionally, thevisible and infrared lasers may be swapped if desired and the parametersof the assembly adjusted appropriately.

Multiple Lasers in a Single Package

Laser diodes that combine more than one laser into a single package canalso be used as the laser light source. This eliminates the need foradditional beam combining elements in the system. For example, SanyoDL-1195-251 provides both a red and an infrared laser in a singlepackage.

Multiple Source Array for 1D Scanning

All the embodiments so far have related to a visible laser point sourceand a IR laser point source bouncing off multiple mirrors, or a singlemirror moving in multiple directions, to create a two-dimensionalscanning pattern where both the X and Y axis of the two dimensionalimaging area is scanned with the single coaxial source of laser light.Rapid scanning causes the eye to integrate this into a single image. Insuch a system, the beams need to be actively steered in both the x and ydirections in the desired pattern. Since there is only reflection fromthe point at which the laser is currently striking, the photo detectorsub system can make inferences about the presence of veins at thatparticular spot on the target.

An alternative embodiment would be to use a linear array of visiblelaser sources and a linear array of IR laser sources which then arereflected off a single mirror moving on a single axis. The effect ofputting these lasers side by side is to eliminate the need to move thelaser point in both the X and Y directions. An appropriate density oflaser sources will be required so that the image presented to the userachieves a desirable resolution. These sources could be from individuallasers for each desired line of resolution or from a lower resolutionarray optically split into a sufficient number of sources to achieve thedesired resolution. Many laser arrays known in the art could be usedincluding a VCSEL array.

Using a laser array, you “paint” an entire field of view with the broadbrush (the array of laser sources). An advantage of this approach is(i), the mirrors are less complex, and (ii) that the collection of thereflected IR light could also be by means of a retro collective mirror.A retro collective mirror has a field of view corresponding to the arrayof lasers, and moves in concert with the movement of the array oflasers. A retro collective unit has a significantly improved signal tonoise ratio since it is only receiving signal input at any given timedirectly in a line of sight with the lasers, thereby minimizing theeffect of ambient light and other noise sources. A retro collectivemirror is inherently larger than a mirror that simply moves the beam.This is to allow for a large light collection area. However due toinertia, as the mirror is made larger, it can no longer be moved as fastas needed for a single laser. This arrangement of multiple lasers allowsthe system to eliminate the fast moving mirror.

As shown in FIG. 5 a, the array of laser light sources 400/408/403, isarranged so that the beams strike the moving mirror 402/406/402perpendicular to the axis of rotation 402 a/407 so that as the mirrorswings back and forth on its axis, the laser beams are scanned so thatthe emitted light forms a rectangle on the target surface 410. FIG. 5 bshows a side view of the arrangement, with the array of lasers 403strike the moving mirror 402 and are reflected in a moving pattern 404.

In addition to the paired visible and IR lasers, the array of laserscould be a single wavelength array of sources that use one wavelength todetect and project as described elsewhere.

In addition to lasers, if the distance to the object being scanned istightly controlled, then LEDs could be used in place of lasers.

Using Light Valves

A device called a grating light valve, such as those made by SiliconLight Machines (http://www.siliconlight.com), can be used in a similarmanner to an array of laser sources. These light valves, typically basedon MEMS technology, are basically mirrors that can be set to areflective or non reflective state. They are typically packaged as anarray of light valves 1506 as shown in FIG. 6.

Referring to FIG. 6, a light source 1500 generates a laser beam 1501which is caused to strike a diffraction grating 1502 which spreads thebeam into a line. Since this line of light is divergent 1503, lens 1504is used to refocus the light 1506 onto the grating light valve 1506. Thelight 1508, with only a single element reflected from the grating lightvalve shown for clarity, is reflected off the grating light valve and isdirected to a moving mirror 1509, which moves along its axis 1510, andis then modulated in the second axis by that moving mirror and isprojected 1511 to the target area. By enabling a single light valve toreflect and all the rest to absorb in synchrony with the movement ofmirror 1509, a single scan line can be painted on the target area. Twoor more of the assemblies in FIG. 6 can be bundled together so that oneor more assemblies are used for visible light and one for infraredlight, or a single assembly can be used for both projection anddetection as will be described below.

This embodiment can also be combined with a retro collective mirrorsystem to enhance the collection of the reflected light.

Single Laser

In another embodiment, the invention uses a single laser that emitslight at a wavelength that is long enough that it is stilldifferentially absorbed by blood but is still visible to the human eye.This embodiment is very important in that it enables building a systemwith only a single laser. All the complexity associated with aligningmultiple lasers is eliminated thereby greatly reducing cost, enginesize, unit size and power consumption.

Light emitted at 635 nm is one possible choice. In this embodiment, thelaser spot performs the dual function of detecting the presence of bloodand displaying that presence of blood to the user. It has beendetermined that a portion of a 635 nm laser penetrates into the tissueand is absorbed by the veins. Accordingly the 635 nm laser can functionsas did the infrared lasers for the purpose of imaging the veins. Aportion of the 635 nm light does not penetrate the skin and is reflectedoff of the skin so that it is visible to the user. This portion of thelight functions as did the visible laser in the dual laser system.

Single Laser Always on

A novel mechanism is used to allow the single laser to be used for bothfunctions. In this embodiment the laser is never completely turned off.Accordingly, even when the image to be displayed is black, the laser isstill powered on at a very low level. The low level is strong enoughthat it can still be detected by the photo detectors so that the devicecan still image the veins, but not strong enough to create a distractingvisible image (so blacks may appear as a faint red color). When theintensity of the 635 nm laser is subsequently increased to project abright portion of the visible image, the gain of the analog circuitryassociated with the received signal (from the photo detectors) isreduced in proportion. Conversely, when the intensity of the 635 nmlaser is subsequently decreased to project a darker portion of thevisible image, the gain of the analog circuitry associated with thereceived signal is increased accordingly. In this manner, the receivedsignal (as measured after the analog circuitry) remains relativelyconstant regardless of the intensity of the projected image.

Referring to FIG. 7 a, a single laser source 70 is oriented so that itsbeam 71 is aimed into a steering assembly 72. This assembly isconstructed as described elsewhere in this patent out of a series offixed and moving mirrors as appropriate to the specific embodiment. Amoving light beam 73 is emitted from the device which then scans thetargeted area of the body 74 in a pattern that is appropriate to thespecific embodiment.

Typically in this configuration, neither repeatability nor knowledge ofthe specific beam position at a given time is required since theprocessing is done in real time as the light beam reads and paints theskin. However, the delay techniques that were discussed previously canbe applied to a single laser configuration.

The photo detector 76 is positioned to measure the light 75 reflectedfrom the skin. Since this is a scanning point source, the reflectedlight is an instantaneous representation of the reflection from a singlepoint 82 on the body. Note that the beam penetrates some distance intothe body so the reflected signal is a composite of both surface andsubsurface features. The output of the photo detector 77 is fed into adetection circuit 78 [that uses techniques that are well known in theart] to determine a change in the amplitude of reflected light andtherefore detecting the relative amount of blood at the point 82 atwhich the laser is currently scanning.

The detection circuit 78 provides an output 79 to the power supply 80 tothe laser source 70. As soon as a vein is detected at the point 82, thepower is increased to the laser source 70 which increases the output ofthe laser so that it is visible to the operator. As soon as thedetection circuit 78 detects that the point 82 is no longer over a vein,then the control output 79 is changed so that the laser 70 outputs alight level that is sufficient for detection, but is no longer visible,or is dimly visible, to the operator. The detection circuitry includesthe functionality to cancel out the increased reflection when the laseris brightened and the decreased reflection when the laser is dimmed sothat the action of projecting the image does not interfere with theability to detect the veins.

If desired, the sense of on and off can be inverted, whereby the laseris brightly lit when no vein is detected and dim when a vein isdetected.

FIGS. 7B-7E provide a representation of the signals being used by thesystem. The reflected signal 90-94 is representative of what is seen atthe inputs 75 and outputs 77 of the photo detector as well as theinitial stages of the detection circuitry 78. The corrected signal 95,96 represents what would be seen in later stages of the detectioncircuitry 78 once the variations in the laser amplitude 88, 89 arecanceled out. The detected vein 97, 98 are representative of the logicin later stages of the detection circuitry 78 as well as the outputsignal 79 from the detection circuitry 78 to the input of the laserpower supply 80. The laser output amplitude 88, 89 represent the outputof the laser source 70, 71 as it is increased and decreased to projectthe acquired image.

Following the reflected signal, at 90 the system is seeing a varyinganalog signal that is representative of a reflection pattern indicativeof a beam that is not crossing a vein. Since different individuals basedon skin color, skin condition and place on the body will reflectdifferent amounts of light as this baseline 90, the detection circuitryis designed so that it can determine this baseline in real time. At 91,there is an amplitude drop off as the beam crosses a part of the bodywhere blood is absorbing sufficient light that the detection circuit 78determines that the beam is over a vein. An internal representation orflag 97 that the beam is over a vein is set and the output to the laserpower supply 79 is changed so that the laser amplitude is increased 89to the bright condition thereby projecting the vein position. Once thebeam is brightened, there is a corresponding rise in the amplitude ofthe reflected light 92. Internally, the detection circuit 78 correctsfor that amplitude 96 to eliminate false readings and to preventsaturation of the detection chain 76, 77, 79.

As the beam 73 continues to move, as long as the reflected levelcontinues within the range for vein presence 92, the laser will stay inits high state 89. The beam will eventually move off of the vein and thereflection will increase once again 93 indicating that the beam hasmoved off of the vein. The detection circuitry 78 will then cause thelaser power supply 80 to return to the dim state 88. The reflectedsignal will now be reduced 94, the detected vein flag will be turned off98. This process will continue to repeat for the duration of scanning.

Single Laser PWM

It is desirable in some embodiments to have greater control over theintensity of the beam when it is being used for detection. In a singlelaser system, it is required that the beam intensity be low enough inthe dark areas of the image so that they appear clearly different fromthe lit areas. It would be desirable in certain circumstances such asdifferent skin coloration or the desire to scan more deeply below theskin to bring the intensity of the light up for scanning. In thisembodiment, the modulation of the laser between detection and projectioncan be in real time where the invention time slices the laser betweendetection and projection so that both functions are performed on thesame pass of the laser over the skin.

In FIG. 8 a such a modulation scheme is shown. The signal 1350 shows thesample period for the photo detector. When the clock is high 1352, thesignal is sampled. When the clock is low 1351, the signal from the photodetector is ignored. The laser output is switched between bright 1354and dim 1359. Dim can also be off in some embodiments. As the beampasses over the body, the beam is kept at a bright intensity 1355 untila vein is detected during the period at 1360. In this example, the veinis seen across two periods 1353. In these periods, the output beam isdimmed 1356/1357 for the portion of the time period that is not used forsampling at the photo detector. It is brought back to its bright level1361 during the sample period of the photo detector. Many variations ofthis scheme are possible including working with multiple lasers ofdifferent colors, and changing the timing of the detection 1352 andprojection 1351 intervals and allowing for multiple levels of bright1354 and dim 1356.

In addition to modulation between detection and presentation modes asdescribed, the laser can also be modulated within each of these domainsto provide for variable detection characteristics such as changing thedepth of penetration and detection through the skin and changing theintensity of the projection intensity to allow for variations in userpreference, ambient lighting conditions and skin color.

Another embodiment of the single laser approach is to time slice thelaser output so that very short pulses of high intensity are emittedfollowed by longer periods of projection intensity. Projection intensityis the light output level that the system wishes the user to see. Veindetection occurs at the bright pulses, but since they are very short,and the eye has a slow response time, they will not perceptiblyinterfere with the desired projection image. The advantage of thisembodiment is that it allows higher intensity for the detection phaseallowing for deeper structures to be imaged and allows the system toadjust for skin characteristics.

Alternating Line & Alternating Frame

The techniques discussed previously for alternating lines and framesbetween detection and presentation in a multiple laser system can alsobe applied in a single laser system.

The use of these delay techniques allows all of the advanced veindetection techniques to be applied by allowing extra time betweendetection and projection as previously discussed as well as theimprovements yielded by the additional control of laser intensityprovided.

Using LEDs Instead of Lasers

As previously discussed a major benefit of lasers was that the beamremains a constant size over a very wide range of distances between thelight source and the surface of the patient's body. An alternativeembodiment can be created that is of lower cost which uses tightlyfocused light emitting diodes (LEDs).

In FIG. 9, a focusing scheme is shown for an LED light source. The LED150 projects an unfocused beam of light 151 on a lens or assembly oflenses 152 which are designed to have a specific focal length so thatthe converging light 153 comes to a point 154 at a useful workingdistance. Beyond the working distance the light begins to diverge 155.

The disadvantage is that the distance between the scanner and the bodysurface will need to be much more tightly controlled than in a laserembodiment. Several controlling mechanisms are possible such as aphysical device that is placed against the skin. One possible mechanismis shown in FIG. 10 a. This approach uses a mechanical device thatincludes an open base 424 that is placed against the skin while allowingthe image to be captured and projected through the opening 425. Theopening can be either closed as shown or open based on the designrequirements of the specific embodiment. The base 424 is connected tothe scan head 422 through one or more separation members 423/424 thatare sized to ensure the proper distance is maintained between the scanhead and the skin. The scan head 422 can be fixed to the positioningdevice or it can be a separate piece that is attached when needed andthen removed.

In an alternate construction, as shown in FIG. 10 b, the mechanism cansimply be a rod 430 of the appropriate length that projects from thescan head so that the distance is maintained when the end of the bartouches the skin 420.

Additional features include:

-   -   1. A lighted crosshair or other pattern projected towards the        skin that becomes crisply focused when the device is being held        at the proper range    -   2. An electronic ranging mechanism such as infrared or        ultrasonic that measures the distance and then emits a set of        tones that indicates that the device is at the appropriate        distance. The tone feedback can be positive—only on when at the        proper distance, negative—only on when outside of the proper        distance or both with separate tones to indicate the two states.

IR Camera, LED Projector

Another useful embodiment of the invention is based on the use of LEDprojection with alternative types of detection. Given the need for tightcontrol to be maintained of working distance, or to provide an autofocus mechanism in an LED embodiment, the detection subsystem can bereplaced with a camera element that is sensitive to IR light and an IRlight source to illuminate the target area. In this embodiment, theimage would be captured using the camera, processed to detect veinpositions within the field of view and an LED implementation asdescribed earlier would be used to project the image back on thepatient's body.

Auto-Focusing in Non-Laser Embodiments

As discussed, a key benefit of using lasers is that they are inherentlyfocused over a wide working range. As discussed above, since LED's donot remain focused over a long working range, the use of LEDs requirestight control of distance to the body area to be imaged. Auto-focuslenses, such as those seen on cameras, could be integrated into thedesign so that a broader working range can be provided. Typicallyhowever an LED implementation is used to minimize cost so that normallythe expense of auto-focusing would have limited application. However,other embodiments of vein enhancement systems such as that described inU.S. Pat. Nos. 5,969,754 and 6,556,858 would benefit from the use ofauto-focus technology and have a cost basis that support such animplementation. FIG. 11 shows an improvement to the device shown in FIG.1 from U.S. Pat. No. 5,969,754. In this figure, an auto-focusing featurehas been added. Computer controllable focusing lenses 1200, 1201, 1202are placed in front of the key optical systems, typically replacing theexisting lenses (e.g. 14). These controllable auto-focus lens systemsare controlled by either the main computing element of the system or aseparate microprocessor dedicated to control functions such as andincluding auto focus. Distance to the body is determined by a rangedetection system 1203, many different types which are well known in theart.

Photo Detector

In addition to the subsystems that project the laser or laser spots onto the patient's skin, a further subsystem provides the detection of thelight that is reflected from both the skin and the subsurface featuresof the patient's body. As previously mentioned, blood rich areas of thebody such as veins absorb light in the infrared spectrum to a greaterdegree than surrounding tissues. The invention uses one or more photodetectors to measure the varying amount of reflection from the target.Light sensitive devices including photo diodes, CCD camera elements andCMOS camera elements and LEDs can be used as the photo detector toperform these measurements. The present invention can implement multiplephoto detectors spatially separated so as to increase sensitivity, andreduce the interference associated with speckle, and specularreflection. However, as mentioned previously, one can achieve areasonable result by using a single photo diode; this will depend on thedesired output and/or operating needs.

The characteristics of the photo detector(s) will vary betweenembodiments. Photo detectors can be selected with narrow bandcharacteristics so that only the detection laser is received by thedetector. This would also have the advantage of making the system lesssensitive to ambient light. Detector characteristics can be determinedthrough selection of the photo detector itself or through the use offilter materials placed in front of the detector. Another alternativeapproach would be to use a photo detector that is sensitive to a broadrange of wavelengths and then by modulating the transmitted laser light,the system would be able to determine which laser, and therefore lightwavelength, was being detected at a given moment in time.

Variations on the Number of Photo Detectors Used

Different embodiments may use different numbers of photo detectors basedon the technical and business needs of the specific implementation. Forexample, a single photo detector might be used to minimize size or cost.Multiple photo detectors may be implemented so that they are spatiallyseparated so that the system is less sensitive to specular reflection.Skin is somewhat shiny and causes unwanted specular reflection. In anembodiment where the photo detectors are separated, they each see thereturned signal from a slightly different angle so that the effect ofspecular reflection is minimized.

The larger the area of a photo diode (one type of photo detector) thelower the speckle noise seen by the system since the random pattern ofspeckles are integrated as a single reflection since they all strike thephoto detector simultaneously. The larger area means that the smallspeckles are a smaller percentage of the total area and therefore haveless of an impact on the signal. However, larger photo diodes have morecapacitance and are therefore slower, which is undesirable in manyembodiments of the invention. By using multiple photo diodes, thedetector area is increased, providing the reduction in speckle noise,without the negative impact on the speed of the detector. This is due tothe smaller capacitance of the smaller photo diode and the fact thateach photo diode being able to have its own pre-amplifier circuit.

A further benefit of having multiple photo diodes is that the receivedsignal is increased without the need for additional amplifier gain andthe associated noise that it would introduce into the system.

A further benefit of having multiple photo diodes is that as the laserpoint moves across the human limb, the curvature of the limb causes anincreasing amount of the light to be reflected away from the scanner asthe beam moves to the sides of the limb. The addition of spatiallyseparated photo detectors adds additional collection area nearer to thespot being scanned and allows more of the reflected light to becaptured. In addition, having two separately placed photo detectorsreduces the impact of specular reflection.

As an alternative to the addition of a photo detector, collectionmirrors can be used in the collection path so that light is collectedfrom spatially separate points and are then reflected on to a singlephoto detector shared by two or more collection mirrors.

FIG. 12 shows an oscilloscope image of the signal received from thephoto detectors. The large ‘humps’ 1700 are caused primarily by thechange in angle as the laser scans across the arm. The amplitude ofthese humps will be affected by the angle at which the beam strikes thearm. A vein signal is also shown 1701.

Array of Photo Diodes

In one embodiment, there is an array of smaller photo detectors arrangedso that there is more collection area towards the outside of thedetection area (where the roll off of signal due to the curved body andthe angle of the laser occurs) and less towards the center where thereflection is more direct and intense. An example pattern is shown inFIG. 13. This could be implemented as a discrete photo detectorsarranged in the appropriate pattern or as a monolithic semiconductorcomponent.

Fresnel Lenses—Tailored Response Over the Field of View

Another technique to control the variation of reflection due to thechange in laser angle across a scan line is to use specially configuredlenses over the photo diodes. In this example a lens is cut from astandard fresnel lens in a pattern that increases the amount ofcollected light as the angle from the center of the photo diodeincreases thereby flattening the received signal.

As shown in FIG. 30, a standard fresnel lens 1750 is cut in a pattern1751 that when placed over the photo detector provides additionalcollection of light reflected from the edges of the scan line and thenrefracts that light into the photo detector.

Electronic Filter

The frequency domain of the signal caused by the angle change as thelaser sweeps is slightly different than the signal caused by thepresence of a vein. Through the use of electronic filters, well known inthe art, such as switched cap filters, the impact of this signal can bereduced early in the signal processing chain, importantly prior to thevein detection circuitry.

Measuring Topology with an Additional Laser

In the prior descriptions, a simplified model of the reflection of thelaser light was presented. In fact, there are varying degrees ofabsorption of light from all of the structures illuminated including theskin, the blood vessels and other surface and subsurface structures ofthe body. Additionally, since the body is a three dimensional structure,the range to the point on the surface being scanned varies in real timeas the imaging point is scanned. For example, the curved shape of thearm would result in less returned reflection towards the edge of the armas that surface curves away from the scanning device. The result is thatthese variable reflections off of these body structures add signals thatmust be filtered out to accurately detect the vein structure.Furthermore, as the beam sweeps across the body, when the beam is at thecenter point of its sweep, the reflected light received at the photodetector is greater than when the angle of the beam is at its maximumdeflection and therefore more light is reflected away from the photodetector.

There many techniques that can be used to eliminate or cancel out theseundesirable signals.

The reflected signal received by the infrared photo detector isrepresentative of both the veins and the surface topology of thepatient's body. Put another way, the surface of the patient affects thereflected infrared signal. This is not desirable in that in mostapplications the user is only interested in the veins of the patient andnot the surface topology. It has been observed that the short wavelengthlight such as blue and ultraviolet are reflected by the skin and ismainly representative of the surface topology of the patient and has novein information contained therein. By utilizing a second coaxial laserlight source at a short but visible wavelength and a second photodetector subsystem for receiving the short wavelength light reflectedsignal, the short wavelength light signal (which contains informationabout the topology of the skin) can be subtracted from the infraredsignal (topology+veins) yielding a signal that is solely the veins(topology+veins−topology=veins). This works in that since the beams arecoaxial, they will be affected by the topology of the target areasymmetrically.

This approach is particularly useful in a system that does not have amicrocomputer for storing a complete image and for performing imageprocessing on that image to enhance the veins (and reject all othertypes of signals) but also has benefit to a stored image system.

Referencing FIG. 14, the coaxial combination of the short wavelength andinfrared laser 528 is projected on to the body surface. Reflected light530 is captured by the photo detectors 526 and 527. Detector 526 detectsshort wavelength light and detector 527 detects infrared light. Thesedetection characteristics may be either a result of one of the signalmodulation techniques described elsewhere herein, component selection orthrough the use of a filter 536, 537 placed in the path of the reflectedlight.

The output of the photo detectors 526, 527 are amplified and conditionedby pre amplifier circuits 631, 632 and then fed through the differentialamplifier 534 which subtracts out the surface topology represented bythe reflected short wavelength light yielding an output 535 that isprimarily based on the reflected vein pattern.

The simplest embodiment would use a red laser for both detection andprojection as described earlier in conjunction with the short wavelengthlaser.

An Implementation with Three Lasers

As a further embodiment, a three laser system can be built to furtherenhance the captured and projected image. In this embodiment, threelasers are used: ultraviolet (e.g., 407 nm for imaging the skintopology), visible (e.g., 630 nm providing the visible light for imageprojection), and infrared (e.g. 740 nm for imaging the veins). Two photodetectors are used. One is for receiving the ultraviolet, and one is forreceiving the infrared light. The ultraviolet laser has absolutely nopenetrating qualities into the skin and therefore the reflection veryfaithfully reflects the patient's topology. This signal is thensubtracted from the infrared signal to yield just the vein signal. Thisembodiment is further advantaged in that the wavelengths of theultraviolet and infrared lasers are very far apart from each other, andtherefore, there is no inadvertent signal pickup by the respective photodetectors.

This implementation would operate in a substantially similar way to whatwas previously described for FIG. 14 with the exception that the coaxiallaser light source 528 would include three laser inputs: infrared forvein detection, ultraviolet for topology detection and a visible colorfor projection. Photo detector 526 would be selected for ultravioletdetection characteristics and/or filtered by 536 to provide selectivedetection of the ultraviolet laser.

Many combinations of multiple lasers and detectors are possible thateach provide optimizations based on the type and depth of structurebeing scanned for, for example adding additional visible lasers foradditional projected information as described elsewhere.

Long Pass Photo Detector Filter, Photo Detector Sees Only IR Light

One goal of the photo detector design is to acquire only the desiredsignal such as the vein pattern without interference from the reflectedlight from other objects in view such as the topology of the body orambient light.

Many techniques are possible. In some embodiments, a photo detector willbe selected that is matched to the wavelength of the infrared laser. Inanother embodiment, a filter that has the ability to block all lightother than the wavelength of the infrared laser can be placed in frontof the photo detector so that only the infrared light passes into thephoto detector. In a third embodiment, the amplitude of the laser lightis modulated either in the time or frequency domain, thereby allowingthe system to know which laser is being seen by the photodetectors. Thethird embodiment has the benefit of allowing a photo detector that iscapable of detecting a broad spectrum of light (e.g., a photo detectorthat is responsive to both 638 nm laser and 740 nm lasers). This allowsa broader range of photo detector devices to be used that are selectedfor other desirable characteristics such as low cost, small size orgreater sensitivity.

Special Laser Handling

As a mirror moves back and forth as it scans the laser beam itdecelerates before it reaches a full stop then reverses direction andaccelerates again. During some portion of the outer extremes of travelthe mirror is moving too slowly for the information returned by thereflected laser to be used. In addition, the output power at theseextremes is more dangerous because it is spread over a smaller area.Therefore reducing or blocking laser power in these extremes helps toensure that it stays within government mandated safety limits.Furthermore, the laser current needed is proportional to the temperatureof the laser. This is important in a battery powered device in that theamount of current needed to run a cooler laser is lower and thereforethe battery lasts longer.

In the preferred embodiment, one or more of the lasers are turned offduring the unused portion at the ends of the scan lines. The benefits ofthis are:

-   -   1. It saves power in the areas that are blind or unusable        because of the slow movement of the mirror    -   2. It reduces overall power used by the laser since it is now        off a percentage of the time, reducing the temperature of the        laser    -   3. It extends battery life    -   4. It is safer, due to less power during the slow moving portion        of the scan    -   5. The active area appears brighter since there is no bright        edge to the pattern caused by the slow moving mirror

An alternative embodiment would leave the laser on all the time, butchange the size of the exit window aperture so that the brighter partsof the scan are clipped off by the window. This embodiment is safer thanthe preferred embodiment in that the failure mode is less likely tooccur, but there is none of the power savings. There are useful benefitsto the internal reflection cause by clipping the output however. Theseinclude:

-   -   1. An internal photodiode can measure the reflected laser light        for calibrating the lasers    -   2. In the case of projecting an image stored in memory,        convergence (the need to know exact laser spot position between        frames) becomes critical. If the laser beam can hit an extra        photodiode when it touches the shade, then that signal can be        used for laser spot position sync. If the shade is also        mirrored, then the extra photodiode can be placed on the top PC        board, to catch the reflected beam.

A further embodiment would be to proportionally reduce the power at themirror slows so that the brightness is kept constant. This would beuseful if a border demarking the edge of the image was desired or ifsome system data was to be displayed in this border area.

Safety

In some embodiments, it is desirable to maximize the output of the laserso that a greater signal or greater penetration into the body is needed.All laser projection devices have governmental safety agency regulationsdictating power output limitations. These limitations are typicallyexpressed as a maximum output of the laser at a given distance from theeye over some period of time. Therefore, a number of techniques thatcontrol power output and the time profile of the output can be used toensure that the device meets these safety criteria.

The balance between high power (yielding brighter images or greater 3dpenetration) and safety are an important part of the design of thedevice.

In one possible embodiment, physical barriers can be placed in thedesign of the product that prevents the user's eye from getting close tothe origin of the laser projections. If a user's eye can not get closeto the source of the laser, the laser power may be increased. Forexample, in an embodiment, protruding bars (think of a football helmetcage) can be placed in the direction of the optical path that preventsthe user from placing an eye too close to the lasers. Accordingly, thelaser power can be increased.

In an alternative approach, signal processing can be utilized to controlthe power output. By way of example, veins have a very distinctivepattern, (e.g., they are tubular shaped). An embodiment can be createdin which the acquired image pattern is stored in a computer memory,image processed to determine whether veins are present, and only uponconfirmation of vein being present is the image projected. In thismanner, the visible laser is not turned on if the unit is aimed at auser's eye (no vein pattern detected).

In a further embodiment, the power of the infrared laser can be setinitially low to detect the presence of surface veins, and only afterthey are detected is the power of the infrared laser increased (to imagedeeper veins) and the visible laser turned on to project the veinpattern.

An additional alternative method is to only turn on the device a when aproximity sensor determines the surface, or eye of a user, is apredetermined distance away from the origin of the lasers, for examplean Agilent HSDL-9100 proximity detector. The power of the laser can beset so that it is safe at the threshold distance. There are many rangedetectors known in the art such based on optical and ultrasonictechniques that can be used in the invention.

An additional alternative method is to turn the lasers on for a shortduration to determine if a vein pattern is in view before turning thelasers on for an extended period to image the vein pattern.

Since the moving mirrors are subject to inertia, they will move moreslowly towards the end of their movement than they do at the center ofmovement. Therefore, the laser intensity over time is higher at theedges than it is in the middle. The system can be designed to manage thebright edges as follows:

-   -   1. In some embodiments, it may be desirable to have the brighter        edges since that helps demark the edge of the scan area    -   2. The housing can be designed so that the exit window clips (or        blocks) the edges of the pattern so the more intense light does        not exit the device    -   3. The electronics can be designed so that the amplitude of the        transmitted laser is reduced near the edges    -   4. The electronics can be designed so that the laser is turned        off near the edges

In all of these embodiments, these techniques can be applied to one ormore of the lasers in the system. Furthermore they can be doneindependently, for example, the visible laser is left on to show theborder line, while the IR laser is shut off at the edges.

Ergonomics

The basic invention provides for the detection of and the projection ofan image of the pattern of blood vessels directly on to the patient'sbody. In this manner, the practitioner has a direct sense of where theveins are and where the center line of the vein is so that they mayeasily and accurately perform venipuncture. One intention of theinvention is to be as easy to use as possible. One expression of ease ofuse is to ensure that the device enhances and doesn't interfere with thenormal work process of finding and accessing the vein.

The integration of the detector and projector into a single device alsoimproves on the Crane patent. In Crane, the vein enhancer implements twoseparate devices, one for illumination and/or trans illumination and aseparate device used for detecting the low light. Such a configurationis awkward and difficult to operate. In addition, having, two separatedevices increases the likelihood losing one of them.

Scanning Activation Techniques

Several techniques can be applied to allow the user to control operatingcharacteristics of the device Such as on/off and gain. This user inputis very important from both a safety and operational standpoint. Thegain of the scanning system will need to be changed based on skin colorand condition as well as the depth of detection desired by the operator.The gain of the projection will also need to be adjusted based onambient light conditions and skin color and condition.

These include

-   -   1. A trigger or switch mounted on the handle of the device in        proximity to the normal position of one of the fingers such as        the thumb. Such an implementation will be described later.        -   a. A trigger or switch that has one position used for on and            off        -   b. A trigger or switch that has two positions, where the            first position puts the device into an aiming mode and the            second begins scanning. This type of implementation could be            useful in an LED or camera implementation where focal length            is limited.        -   c. A trigger or switch that has two positions, where the            first position is for low gain, and therefore short            penetration, and the second is for high gain.        -   d. A trigger or switch with a single position that can be            tapped multiple times to change the gain of the system    -   2. A slide switch trigger, where multiple positions along its        travel change settings on the device    -   3. An analog trigger as in a video game joy stick, where the        distance of the pull on the trigger is used to change settings        of the device    -   4. A pressure sensitive switch where pressure is used to change        settings on the device    -   5. A rolling thumb control where rolling the wheel in one        direction reduces gain and the other direction increases gain    -   6. Any of the above implemented such that the switch stays in        position when it is released and must be manually reset to an        off position    -   7. Any of the above implemented as a dead man switch such that        as soon as pressure is removed from the switch it returns to the        off position.        Gravity Tilt for Aiming Projection on Skin.

In the present invention there are described a number of novelmechanisms to automatically maintain the position of the imaged area asthe practitioner moves the needle to perform venipuncture. It will beappreciated by those skilled in the art that the present invention isnot limited to locating veins, arteries and other blood-rich structuresand either implicitly or explicitly focused on placing a needle into thestructure. There are many procedures, such as an intramuscularinjection, where it is desirable not to puncture a vein. The inventioncan be used to avoid hitting a vein in this case.

Gravity Adjusted

One such mechanism is to mount the imaging head on pivot-able mechanismmounted to the needle protector. The mechanism is arranged so that theforce of gravity biases the projection angle at a predetermined angle tothe earth's surface. As the needle is moved, the field of view continuesto remain at a constant angle to the surface of the earth.

Computer Control Using Orientation Detection

Another mechanism would be to use electronic devices including tiltswitches and/or accelerometers to monitor movement of the scanningelement. A mechanism such as a switch press could be used by thepractitioner to indicate that the scanner should go into a mode where itattempts to maintain the field of view on a fixed position on the body.As movement is detected, the device moves the scan area to compensatefor the practitioners hand movement.

Several movement control mechanisms are possible. In one embodiment,positioning actuators can move the scan element in two dimensionsthereby moving the imaging/projection area. In another embodiment, theinternal mirror arrangement can be such that a bias is added orsubtracted from the mirror's travel, thereby changing where theprojected image is placed. In another embodiment, a combination of bothtechniques can be used. In another embodiment, an engine with higherthan necessary resolution for vein location can be used and a window ismoved within the higher resolution space.

Computer Control Using Feature Detection

The previous embodiment relies on the system detecting a change in itsposition by measuring the movement of the scan head. In anotherembodiment, as the image of the vein structure is captured, the systemcan identify unique patterns in the structure of the captured image. Forexample, the system could look at a cross point between two veins. In aframe to frame comparison, the change in position within the imagingfield of this unique pattern can be determined and then the scanposition can be moved by one of the techniques previously described sothat the unique pattern is kept in a constant position within theimaging field of view.

Florescent Cream on Skin

In the embodiments previously described, the projection of the imagerelies on repeated scanning of a visible light source over the area ofthe body being scanned. It is known in the art that there are materialsthat emit visible light when energized by a violet or ultraviolet lightsource. These materials can continue to emit light for a period of time,up to several minutes, after the energizing light source is removed.Furthermore, these materials can be mixed into a gel, cream or liquidbase so that it can be applied to the surface of the skin. In addition,the florescent material can be combined with the antiseptic that isalready used in venipuncture.

An embodiment of the invention can be made where a violet or ultraviolet laser (e.g., 407 nm) can replace the 630 nm laser. Thepractitioner can apply the florescent material to the surface of theskin and then the scanner can be passed over the area to scan the veins.The device uses the violet/UV laser to activate a pattern that matchesthe vein position on the treated skin.

This embodiment is very useful and unique for several reasons. First,the image of the vein position is maintained even after the device isturned off and put away, thereby freeing both hands for thevenipuncture. Secondly, the size of the imaged area is now limited bythe area that the florescent material is applied to, not by theprojection area of the device. Third, if the procedure is taking toolong, the image can be reactivated by rescanning the area.

Still further, a three laser system can be built, comprising a visiblelaser for presenting the vein image and a near IR for detecting theposition of the veins and a violet/ultra violet for energizing theflorescent materials. All lasers are arranged to project along a singleaxis. Without the violet/ultra violet laser turned on the systemoperates as described in previous embodiments. However, once anacceptable image is viewed; the 407 nm can be energized to paint thesame image as that projected by the 630 nm laser, thereby energizing theflorescent material to emit the vein image.

It is known in the art that there are chemical dyes that can changecolor by exposure to light. Such a material can be substituted in theabove embodiments in place of a florescent material.

Distance Aware User Interface

Several control mechanisms that can be used to adjust various operatingparameters for the unit are previously described. Another embodiment isto use sensors well known in the art to determine distance to the bodysurface being scanned. For example, an IRDA module typically used in alaptop computer could be used to sense distance by using the amount ofreflection from the IR led back to the photo sensor as a proxy fordistance.

These can be added to the device or in a preferred embodiment, theaverage intensity of one or more of the lasers already in the device canbe used to approximate the distance based on the amount of lightreflected. This average intensity would vary based on distance.

When the scanner is close, say 6″, the scanning angle can be set tomaximum and the IR power, signal gain and differentiation levels are setto medium. As the scanner moves away from the body, the scanning anglecan be reduced in proportion to the distance. In this way, if the targetwere for example the arm, the scanned area would not grow as distanceincreases. This would prevent wasting detection area by preventing theimaged area from growing bigger than the arm.

When unit is moved closer than 6″, the level of differentiation, andgain is increased. This is OK to do at close range but at far distancesthis would cause more false positives—veins would be indicated in placesthat they do not exist. However, at close range this will show deeperveins. This provides a very intuitive user experience. Move closer—seedeeper. Other inventions that use fixed focal length systems andtherefore must be kept at a single distance from the body cannot providethis user interface.

Electronics

Time Division Multiplexing Two or More Lasers

In the system design, the photo detector can be selected or filtered sothat it is responsive to the infrared laser but not the visible laser.In the manner both lasers can be on at the same time without having thevisible laser couple into the photo detector. In some cases, usefulattributes of a photo detector such as size or cost would make itpreferable to use a photo detector which is responsive to both thevisible laser and the infrared laser. In this embodiment, both of thelasers can be pulsed on and off at high rates without affecting theapparent quality of the image (visible light projection) or the qualityof the acquired image (the reflections of the IR laser). Bysynchronizing the two lasers so that while one is on, the other is off,the image acquisition circuits (photo diode and amplifiers) can bearranged to only see signals from the appropriate laser. In this mannerthe other lasers do not interfere at all with the signal acquisitionapparatus.

Frequency Modulation of Lasers

Through the use of amplitude modulation on the transmitted laser, simplefilter circuits can be used in the photo detection subsystem to allowone or more laser signals to be differentiated from ambient light andfrom other laser signals in the system. In FIG. 8B, the laser outputsignal waveform is shown with two levels, bright 1370 and dim 1372. Forexample, in a single laser system, the bright signal might be used toproject and the dim signal would be used to scan. Furthermore, the dimcould also be an off state for the laser and this implementation wouldstill be effective.

In the photo detector subsystem, the output of the photo detector can beDC coupled so that no low frequency or DC bias signals pass through tothe next stage in the circuit. In this manner, any light, includingambient light, that doesn't exhibit the high frequency modulation, isnot seen by subsequent stages of the circuit.

Another mechanism to differentiate between lasers is shown in FIGS.8C-8E. In this embodiment, the lasers are amplitude modulated atdifferent frequencies causing the reflected light received at the photodetector to also be frequency modulated. The visible laser 1380 ismodulated at one frequency and the infrared laser 1383 is modulated atanother. The light received at photo detector 1381 is a combination ofthe reflected light from both lasers. The received signal is fed throughtwo different band pass filter circuits. The circuit at 1382 selects forone frequency and the circuit at 1385 selects for the other. Thereforethe signal at 1384 and 1386 are representative only of the lightreflection from one of the lasers. This can be implemented in a singlecircuit so that only the infrared vein signal is seen or in two or morecircuits where both an infrared vein signal is seen and a longwavelength topology-detection signal is received. A whole range of highpass, low pass, band pass, band block and notch filters can be usedbased on the technical and business needs of the specific embodiment.

User Adjustments

The system can be arranged as either a binary system or grayscalesystem. In a grayscale system, the infrared laser signal received by thephoto detector is simply echoed and re-transmitted by the visible laser.In this manner, various levels of intensity can be shown. Accordingly,the image of a vein may vary in intensity as a function of the magnitudeof signal received.

In a binary system, the projected image is either on or off. Todetermine whether the projected image should be on or off, a comparatorwith a trip point is placed after the photodiode. If the signal crossesthe trip point the visible laser is turned on and when it falls belowthe trip point it is turned off.

The system can set these parameters automatically based on built-in rulesets or a user input device like a dial, or push buttons, or any othermeans of user input could be placed on the device, and the user manuallyadjusts the trip point (essentially making the device more or lesssensitive.)

Some of the parameters that will often need to be controlled to dealwith patient and environmental variability include:

-   -   1. Laser intensity        -   a. Visible for projection brightness        -   b. Infrared for penetration depth    -   2. Persistence of vein lock    -   3. Selection of vein size to detect    -   4. Working range and focus distance    -   5. Field of view size    -   6. Mirror amplitude        IR Modulation Analog or PWM (Pulse Width Modulation)        Throughout all the embodiments, when we discuss adjusting the        power of a laser, such adjustment could be made by either        adjusting the current to the laser, or alternatively, modulating        the laser on and off at a rapid rate (pulse width modulation or        PWM). Depending upon the duty cycle, the average laser intensity        will be changed. With respect to the visible laser, the human        eye integrates the signal and, provided the frequency of the PWM        is faster than the eye integration time, the laser will appear        as if it was always on, but brighter or dimmer as the on cycle        time increases respectively.

The system will also need to adjust the power of the infrared laser.This can be done by adjusting the current to the laser, oralternatively, by PWM. Provided that the PWM modulation is faster thanthe response time of the receiving means (photodiode plus amplifiers),the modulation will have the same effect upon the received signal as ifyou reduced the current to the laser.

Simplified Scanning

There are various methods that can be employed for creating a scannedlaser pattern. In many embodiments, it is desirable for the scan patternto be the same from frame to frame and for the system to be able todetermine the instantaneous position of the lasers. Such animplementation would allow time consuming processing and integration ofdata across frames to occur.

In general however, the lower level of position precision that isrequired, the easier it is to produce the pattern, the lower the systemcomplexity becomes and the lower the cost becomes. In an embodimentwithout image memory, since one does not need to remember the specificsignal at a specific position over time, there is no need for areproducible scan pattern. Therefore, from frame to frame the laser scanlines do not need to fall reproducibly upon the scan lines of the priorframe and there is no need to know the instantaneous position of thelaser. The reason one does not need a reproducible scan pattern orinstantaneous position information is that the visible light iscoaxially aligned to the infrared laser. The visible light is a functionof the received image in real time. Accordingly, whatever location isbeing imaged is instantaneously being projected.

Scan Amplitude Modulation Scanning

One such simplified modulation scanner which is well suited to thisinvention is amplitude modulated circular mirror. In this case a mirroris arranged to run at resonance in a circular or oval pattern. Themagnitude of the circle is then amplitude modulated at a rate highenough to avoid appearance of flicker. Accordingly, a scan pattern isformed which starts with small concentric circles and grows sequentiallylarger until reaching a limit and then collapses sequentially to thesmallest circle.

Such a pattern has many advantages over a traditional raster scanpattern. Rather than a rectangular shape which would be typical of araster scan, this method can be used to generate circular or ovalpattern shapes. The mirror in this design is always moving and the laseris always actively painting—there are no required off times as themirrors move into position for the next scan line. The pattern can beadjusted so that it spends more time scanning near the center of thepattern so a brighter, denser, better defined image appears in thecenter of the scan area. Additionally, the mirror operates at resonancewhich provides the lowest power dissipation, which is important inhandheld battery operated devices.

System Gain Adjustment

It is necessary to adjust the gain of the system during operation inorder to ensure that the amount of reflected light is within the properoperating range of the photo detectors.

One method of adjusting the gain is to maintain a constant output fromthe detection laser and adjust the gain of the photo diode amplificationcircuitry so as to get an appropriate signal that is neither too low fordetection nor too high so that the photo detector or circuit saturates.This approach can become fairly complex due to the speed requirements ofthe gain adjustment.

Another method is to fix the gain of the photo detection circuitry butadjust the power output of the IR laser so that an appropriate signal isoutput from the photo detection circuitry (once again not to low orsaturated). It is much easier to design circuits that adjust the IRlaser due to the extremely high modulation bandwidth of the lasers. Aspreviously discussed, the laser can be adjusted either by analog ordigital means.

A laser must be calibrated in that its intensity is sensitive to ambientconditions such as temperature. Some laser diodes have internal mirrorsto perform the calibration. An alternative technique is to use thehousing of the scanner to block a portion of the light, perhaps an outerscan line and reflect that light back to the photo detector. Thatreflected light can be used for calibration.

Stored Image, Allows Multi-Scan Averaging

In some embodiments of the invention, the system will have amicroprocessor and memory buffer so that the reflected light from thescanning laser will be kept as a representation in memory. By averagingthe image over multiple scans, the system can form an image with greaterresolution than it could have by only using a single pass of the laser.In order for this to be done, the system needs to ensure that the imageelements being captured from scan to scan represent the same physicallocation on the patient.

The benefit to the system design is that the gain of the photo detectorand subsequent analog circuits can be reduced.

There are several ways to do this. One is to provide a mechanicalstabilization, similar to what was described for the LED implementation(FIG. 10). Many techniques for mechanical, analog and digital imagestabilization are known in the art and can be applied to this inventionsuch as best fit correlation.

For example, you can identify a specific point or a group of pointswithin the image in a single frame, for example the cross point betweentwo veins. The system can then adjust the position of the image fromframe to frame so that the image elements averaged together representthe same position on the body.

Windowed Vein Tracking

Since veins are linear structures, a novel technique can be used toaccurately identify veins and to separately highlight one or more veinsand ignore others without using image memory or signal processingtechniques. Referring to FIG. 15, a schematic representation of an arm1809, is shown along with a simplified pattern of veins 1802/1814. Asshown, veins are roughly linear structures. Normally, depending on thepart of the body the practitioner is attempting vein access, only veinsthat are oriented in a single direction are typically used to administermedicine or draw blood. For example, on the arm, the veins that runalong the long axis of the arm are typically used. Therefore scanningthat favors vein detection along that axis is desirable.

A series of scan lines are shown 1806, 1810 and 1813. Each scan lineoccurs sequentially in time with 1806 first, 1810 second and 1813 last.This technique relies on the fact that once a vein's position is foundon a scan line, an assumption can be made where the vein is likely to beon a subsequent scan line. The vein signal can be expected to occurwithin a small distance to the right or left of the position seen on theprevious scan line. Therefore the system can apply a windowing techniquewherein vein signals that occur outside the window are given a lowerpriority or are ignored completely

Referring to FIG. 15, a signal diagram to show the windowing approach isprovided. 1804, 1808, and 1812 are the reflection signals from scanlines 1806, 1810 and 1813 respectively. In this drawing, a high signalrepresents greater absorption of the laser light at that point on thebody. 1807, 1811 and 1813 are the “windows” calculated based on 1804,1808 and 1812 respectively. In this drawing, when the window signal ishigh, detection occurs, when it is low, no detection occurs.

The signal 1800 is caused by vein 1814 and signal 1801 is caused by vein1802. This simplified example is for a system that is designed to onlyshow the single largest vein in the field of view. By using a systemcapable of keeping track of multiple windows, multiple veins could betracked. Alternatively, the sense can be inverted and the vein withinthe window could be ignored.

Vein 1802 is selected as the vein of interest by some criteria, set inthe system or by the user, such as size of vein or the central locationof the vein in the field of view. Based on the vein's position asdetected by the pulse 1801 on the reflection signal 1804, a windowsignal 1807 is created that ignores vein reflections that occur outsideof the detection window 1805 on the next scan line 1810/1808. Referringto signal 1808, vein 1814 is ignored since it falls outside the windowand vein 1802 is detected since it falls within the window. However,since the vein is traveling at an angle with relation to the scanpattern, the vein is now offset within the window. In order to track thevein on subsequent scan lines, the system now re-centers the window 1811so that when it is applied to the next scan line 1813/1812, the veinfalls within the window. This process repeats for the entire field ofscanning.

A user interface can be implemented allowing the user to select a numberof veins to detect simultaneously and to switch focus from vein to vein.Also, the user could control the width of the window to optimize thedetection of the vein. Additionally, the user can turn this feature onand off so that they can either see all veins or just a specific vein orveins. Since there is inherent directionality to the procedure, the usercan rotate the scanner to see only those veins at a particularorientation.

Diagrammatic Walkthrough

Walk Through of the Engine

In FIGS. 17 through 22, an embodiment of the device is presented. Thisimplementation uses two lasers, one infrared and one red. The lasers aremade coaxial through a series of bounce mirrors and are combined by adielectric mirror. Two moving mirrors are used to move the beam in araster pattern which then exits the engine and strikes the patient'sbody. The collection path includes two spatially separated photo diodes.The electronics use an analog, real time approach whereby the detectionof a vein causes an immediate reduction in the projected visible lightat the point at which the vein is detected. The operator sees thispattern of dark lines directly on top of the position of the veins.

Referring to FIG. 17, the scanning engine is shown as an assemblyincluding a detector deck 1004, an optical deck 1005 and a circuit board1006. Both mechanical and electronic parts are mounted on these boards.The engine is oriented so that the laser scanning pattern 1000 projectsperpendicular to the boards through an orifice in the detector deck1004. The photo detectors 1001-1002 are aimed along the same axis sothat they have a clear view of the reflected light.

In FIG. 18, the visible laser diode 1015 and infrared laser diode 1019are arranged for best fit within a miniature form factor of the engineand therefore rely on a series of bounce mirrors to realign the beam.Both laser diodes are mounted to holder assemblies 1023/1024 and heatsinks 1016/1018. Proper thermal management of the diodes extends theirworking life and increases the reliability of the engine.

An optional connector 1017 is mounted to the side of the engine to allowit to be used in an embodiment of the device that allows the scan headto be removed from the portable handheld device and mounted on analternative base such as a tabletop stand.

The detector deck 1020 is a printed circuit assembly that holds thephoto detectors 1021/1022 as well as other electronic componentsnecessary for the operation of the engine. For example, thepre-amplifier circuitry for the photo detectors will typically bemounted in close proximity to the detectors 1021/1022 so that noise inthe system is minimized.

The photo detectors 1021/1022 are shown with integrated dome-shapedlenses to increase sensitivity in the direction of the reflected laser.Various schemes both with and without lenses can be implemented inengine embodiments. In addition, filters can be placed in front of thephoto detectors so that the wavelength of light they respond to can bespecified.

In FIG. 19 a-c which is an illustrative example, several views of thebounce mirror assemblies are shown. Since the intent of the design is tomake two or more laser beams coaxial, proper alignment is critical.Shown is one of the exit windows from the laser diode 1038 with the beam1037 striking the mirror 1040 thereby reflecting the beam into the newdesired orientation 1042. The mirror is held in position by anadjustable holder 1041.

The holder assembly 1041 is comprised of a fixed platform 1031 that isfastened to the optical deck in a fixed manner. The mirror 1032 isattached to a wedge 1034 that is angled in the desired manner to reflectthe beam in the appropriate direction. The wedge is fixed to a floatingdeck 1033 which is attached to the fixed platform 1031 through a numberof screw 1035 and spring 1036 assemblies. The spring 1036 is placedaround the screw 1035 and is compressed by the two platforms 1033/1031so that the springs provide a constant force against the two platformsensuring that they are held as far apart as the screws will allow. Thescrews (e.g., 1039) pass through an unthreaded hole in the floating deckand into a threaded hold in the fixed platform 1031. By tightening orloosening the screws, the decks are moved closer or further apart.Through the use of multiple screws, several degrees of freedom ofadjustment are obtained, thereby allowing the beam to be properlyaligned along the desired path.

In this design, three of these bounce mirror assemblies are used. Thisdesign uses mechanical screws to fine tune the position of the mirrorsand in practice would be locked in place once positioned with anadhesive material such as locktite. High volume configurations of theproduct could use robotic assembly and the mirrors would be positionedand then welded, epoxied or glued into place eliminating the cost andcomplexity of the screw/spring assembly.

Referring to FIG. 20, the path of the laser beams are shown. Many partshave been removed from the diagram to allow the beam path to be easilyseen. The laser diode 1080 emits a beam 1081 which strikes the angledmirror and is reflected along path 1083 which then strikes thedielectric mirror 1084. The mirror's characteristics are selected sothat this beam passes through mirror 1084 and exits along path 1085.

The second laser 1088 emits its beam along path 1089 which then isreflected off of mirror 1090 along path 1091. The beam 1091 strikes thedielectric mirror 1084 which as been coated to reflect the wavelength oflight emitted by laser 1088. Therefore, the beam is reflected along path1085. At this point the two lasers are now coaxial. The beams 1085 arereflected off of mirror 1086 and are reflected along path 1087 so thatit strikes the moving mirror that is part of assembly 1087. Thisfast-moving mirror is oriented to provide the x-axis scanning. The lightis reflected onto the mirror in assembly 1092 which is a slower movingmirror that provides the scanning in the y-axis. In this diagram, theresulting scanned beam pattern exits out towards the back of thedrawing.

In FIG. 21, which is an alternative view of the previous drawing, thescanned laser beam exit pattern 1095 is seen more clearly.

In FIG. 22, additional novel features of the design are seen. The laserdiode mounting bracket 1152, is a split ring design. The screws 1159pass through unthreaded holes in the bracket 1152 and into threadedholes on the optical deck 1160. By tightening the screw on the splitside of the bracket 1152, the laser diode assembly 1158 is compressedand held in place. This allows the position of the diode to be locked inboth an in/out orientation and in rotation. Locking the rotationposition is critical in designs that use the laser's polarization ratherthan wavelength for beam alignment.

The engine uses extensions 1153, 1155, 1157 on the circuit board toprovide mounting features so that the entire engine assembly can befirmly mounted into a housing. The extensions could also have been onthe detector deck or optical deck or on one or more of the mechanicalcomponents of the engine. Holes such as 1154 are provided so that eithera screw or a boss can be used to align and hold the engine in thehousing. The extensions can be held in place with screws or bycaptivating them in a feature of the housing. The extensions can be madein a range of shapes so that they do not interfere with features in thehousing. For example, the notch 1156 is designed so as not to interferewith a boss in the housing.

In the current design, the high speed mirror 1111 is implemented with aTexas Instruments TALP3400 and the low speed mirror 1111 is implementedwith a Texas Instruments TALP4500. The red laser diode 1111 is a SanyoDL-LS 1148 and the infrared laser diode is a Sanyo GH0781JA2C. The laserlens 1111 is a Thorlabs, Inc. 350150-B and the photo diodes 1111/1111are Hamamatsu S6968-01.

Referring to FIG. 23, one embodiment of a portable handheld vein scannerbased on the engine described previously described. It will beappreciated that this device is just one example of the design of thepresent invention and that the shape and features can be altered to fitthe end user's needs while still employing the teachings of the presentinvention. This embodiment is typically a two piece design with adetachable head 1605 connected through a friction fit; a snap onmechanism or other suitable means to a handle 1606. The buttons 1610,which are on both sides of the handle, are designed so that when theyare pressed, latches that hold the scan head and the handle together arereleased and the user can separate the two pieces. Screw holes 1600 onboth sides of the handle are provided along with matching internalbosses in the scan head allow the handle and head to be permanentlyattached should the deploying organization wish to prevent theseparation of the parts.

The handle is composed of a top housing 1608 and a bottom housing 1609that are snapped and screwed together to form a single unit. The batterydoor cover 1607 completes the handle package. This door cover 1607 isdesigned to be removed by the user with the latch 1607. There is alsoprovision for a screw hole in the battery door and a matching hole inthe inner housing should the deploying organization wish to prevent theend user from accessing the battery.

In the top portion of the handle, two LED openings are provided 1603,1604. These are illuminated by LEDs on a board inside the handle andprovide important status information to the user. The openings at 1603and 1604 can be filled with a light pipe or pipes to bring the light upto the top surface and can be covered either with a molded light pipe orwith a label that fits into the opening at 1612. An inset area isprovided at 1602 that allows for a label to be positioned providing acompany logo, a product model identifier or other user viewable indicia.Since the top and bottom are separable, it may be desirable to repeatidentical or other labeling information on the handle part as well.Additional labels can be placed on the inside of the battery door,battery compartment or on or near the scanner opening on the other sideof the scan head 1605.

As seen in the engine design discussions, thermal management of thelaser is critical to minimizing power consumption and life of the laser.Therefore, openings 1601 are provided on both sides of the scan head toallow convection cooling of the scan engine. In certain embodiments, itmight be desirable to have a fully sealed unit. In this case, theopenings will be eliminated and other techniques well know in the artwill be used to cool the lasers. For example, the heat sinks on theengine can be continued on the outside of the housing.

Views of the handle 1620 separated from the head 1621 are shown in FIG.24. 1630/1631 are the matching screw holes for the optional screws 1600.These holes are designed to engage the threads on the screws. The holes1627/1628 line up with these holes and do not engage the threads, butare designed so that the screw heads apply pressure against the head andhandle thereby keeping them connected.

Further screw holes are seen at 1634, 1633, 1632 that hold the top andbottom plastic pieces of the scan head together. Internal mating bossesare provided in the lower half of the scan head housing.

Mating latches 1626/1625 and holes 1623/1624 hold the scan head andhandle together. The latches 1625/1626 are internally sprung so thatwhen the buttons 1610 in FIG. 23 are not pressed, they captivate theoutside edge of the slots 1623/1624. When the buttons 1610 are pressed,they no longer engage the slots 1623/1624.

Two mating electrical connectors 1635 and 1622 are provided so that thebattery, switch and other electronics in the handle 1620 connect to theelectronics in the head 1621. A shoulder 1637 and a matching inset 1636are provided to ensure proper alignment of the connectors as the headand handle are separated and re-connected.

In FIG. 25, the head and handle are shown attached. A trigger thatallows the user to control the operation of the scanner is shown at 1655and 1662 (See FIG. 26). This trigger is molded as part of lower housing1653 and internally comes in to contact with an electrical switch. Thehinged part of the lower housing that forms the trigger 1655 is designedso that it has an appropriate level of force so that the user doesn'taccidentally trigger the unit but doesn't have to press to hard either.The mating electrical switch is selected so that the user gets positivetactile feedback of the switch closure.

The lenses for the photo detectors are shown at 1650. They are alignedin the same plane as the emitted laser path 1651 so that they can pickup the reflected light from the target area. In FIG. 26, the photodetectors 1660/1663 are shown arranged around the laser exit window1661.

FIG. 27 a is shown with the lower housing of both the handle and thehead removed FIG. 27 b showing the position of the scan engine 1670, thepaired electrical connectors 1674 and the electrical switch 1671 thatwere described earlier. A PCB 1676 is show holding the switch, the LEDsand the connectors 1674 previously described. A second PCB that mates tothe battery connectors is at 1673.

The battery door spring mechanism is shown at 1675. The loop in themechanism provides force in the forward direction (towards the head)thereby engaging the latch. A second view of the door and the latchmechanism is shown in drawing 27 b with the tongue 1697 that engages thehandle top housing 1698 and the clip on the latch 1700 that engages thehandle top housing at the other end of the battery door.

One of several screw bosses 1695 is used to connect the top and bottomhalves of the housings. Furthermore, an alignment standoff is shown at1699.

Referring to FIG. 28, which shows the cavity/rear housings of both thehead 1685 and handle 1686, several additional details are revealed.Bosses 1691 and 1687 provide mounting for the mounting tabs on the scanengine described earlier. These can be secured with screws or can becaptivated between the two halves of the housing. An alternative designcould captivate the engine in shock absorbing materials to increase theruggedness of the device.

Further detail of the spring latch mechanism described earlier can beseen at 1688 and the contact point/stud for the electrical switch fromthe trigger is shown at 1690.

Ribbing that performs the multiple function of strengthening the housingand locating the battery is shown at 1689 and 1692.

Referring to FIG. 29, a block diagram of the invention is presented. Theelectronics system 1747 can be based on discrete electronic componentsor can have one or more microprocessors and memories 1748. In thisembodiment, a small processor with on chip memory is dedicated tohousekeeping functions including laser calibration, proximity sensing,and other system control and setup functions. Additional processing andmemory components can be added to perform higher level functions likeimage-based vein detection.

In this embodiment, a raster pattern is implemented. A mirror drivesubsystem 1738/1733 is controlled 1738/1735 by the electronics to drivethe X mirror 1740 at a higher speed than the Y mirror 1734 to create theraster pattern. The electronics will control mirror on and off, and themirror will report back when it begins its scan. The mirror drivesystems 1739/1733 provides the drive waveform to the mirrors 1740/1734that cause them to oscillate at the proper speed and in synchrony. Thisconsists of sine wave to the mirrors. The drive circuitry also containsdetection circuitry that uses a feedback path 1737/1736 from the mirrorsto detect that the mirrors are in motion. In this manner, if a mirrorhas failed to move, the engine can shut down the lasers to ensure usersafety.

The lasers are also controlled by the main electronics 1747 through aset of drive circuits 1746/1742. These circuits provide the ability toset the intensity of the lasers 1744/1741 from off through maximumintensity. In this embodiment, the lasers contain internal mirrors forcalibration and which are read back from the lasers 1745/1743 andthrough the drive circuits 1748/1750 into the main electronics. Thereverse path is used to control the drivers and lasers.

In this embodiment, a proximity sensor 1725 to detect that there is asurface within working range. The main electronics reads 1729 the sensorto ensure that the lasers are not turned on if there is an object eithertoo close or no object within proximity of the front face of thescanner.

The photo detection subsystem consists of a pair of photo diodes 1727and an amplifier 1726 that is fed through 1730 the main electronics forvein detection. A control for setting gain is provided through 1730.

Since this is a portable device, power is provided from a battery 1731,which provides 1752 power to a control circuit 1732 which providesvoltage regulation and delivers 1751 the appropriate voltages to theelectronics

We claim:
 1. A vein imager, for use in imaging subcutaneous veinsbeneath a target surface, said vein imager comprising: one laser, saidone laser configured to emit a beam consisting of light at a selectivered wavelength; one or more mirrors, said one or more mirrors configuredto receive said beam of light from said one laser, said beam of lightthereby reflected onto the target surface to create a spot of lightthereon; a mirror drive system, said mirror drive system configured todrive said one or more mirrors to move, to drive said spot of light toselectively move upon the target; means for instantaneously measuringthe amplitude of said selective red wavelength of light reflected fromsaid spot, throughout selective movement upon the target; a drivecircuit, said drive circuit configured to receive said instantaneousmeasurement of said reflected light amplitude of said spot from saidmeans for instantaneously measuring, and to determine a change in saidinstantaneous amplitude of reflected light from said spot throughoutsaid selective movement; wherein said drive circuit is configured tochange an amount of power to said one laser from a first power level toa second higher power level, when said drive circuit detects a decreasein said instantaneous amplitude, being characteristic of a detectedsubcutaneous vein location; and wherein said drive circuit is furtherconfigured to decrease the power to said one laser to be at said firstpower level, when said drive circuit detects an increase in saidinstantaneous amplitude, being characteristic of no detectedsubcutaneous vein locations.
 2. The vein imager according to claim 1,wherein said drive circuit is further configured to store a flaggedamplitude, for use in eliminating a false indication of no detectedsubcutaneous vein locations, wherein said flagged amplitude is set tomatch said instantaneous measurement of said reflected light amplitudeof said spot, after said change in said amount of power to said secondlevel, and wherein said drive circuit is further configured for saiddecrease to said first power level to occur when said drive circuitdetects said increase in said instantaneous amplitude, wherein saidincrease is relative to said flagged amplitude.
 3. The vein imageraccording to claim 2, wherein said selective movement of said spot uponthe target comprises movement in a pattern.
 4. The vein imager accordingto claim 3, wherein said mirror drive system is configured to drive saidone or more mirrors to selectively move to repetitively drive said spotof light in a sequentially growing and collapsing pattern.
 5. The veinimager according to claim 4, wherein said mirror drive system isconfigured to drive said one or more mirrors to drive said spot of lightin said sequentially growing and collapsing pattern at a rate of atleast 30 Hz.
 6. The vein imager according to claim 5, wherein saidsequentially growing and collapsing pattern comprising a pattern fromthe group of patterns consisting of: an ellipse pattern; a circlepattern; and a spiral pattern.
 7. The vein imager according to claim 6,wherein said selective red wavelength of light is in the range of 620 nmto 750 nm.
 8. A method of imaging subcutaneous blood vessels beneath atarget surface, said method comprising: emitting a beam of light, usingone laser, said beam of light consisting of light at a selective redwavelength; receiving said beam of light from said one laser upon anarrangement of one or more movable mirrors, and thereby causing saidbeam of red laser light to create a spot of light on the target surface;moving said one or more movable mirrors, using a mirror drive system,for directing said spot of light to selectively move across the targetsurface; measuring the instantaneous amplitude of said selective redwavelength of light reflected from said spot, throughout said selectivemovement; determining the occurrence of a change in said instantaneousamplitude of reflected light throughout said selective movement; causingan increase in an amount of power to said one laser when a decrease insaid amplitude is determined to have occurred; and causing a decrease insaid amount of power to said one laser when an increase in saidamplitude is determined to have occurred.
 9. The method of imagingsubcutaneous blood vessels according to claim 8, further comprisingeliminating a false indication of no detected subcutaneous veinlocations by setting a flagged amplitude to match said instantaneousmeasurement of said reflected light amplitude of said spot after saidincrease in said amount of power, and causing said decrease in saidamount of power when said increase in said amplitude is determined tohave occurred relative to said flagged amplitude.
 10. The method ofimaging subcutaneous blood vessels according to claim 9, furthercomprising selectively moving said spot in a pattern across the target.11. The method of imaging subcutaneous blood vessels according to claim10, further comprising repetitively driving said spot of light in asequentially growing and collapsing pattern.
 12. The method of imagingsubcutaneous blood vessels according to claim 11, further comprisingrepetitively driving said spot of light in said sequentially growing andcollapsing pattern at a rate of at least 30 Hz.
 13. The method ofimaging subcutaneous blood vessels according to claim 12, furthercomprising repetitively driving said spot of light in a sequentiallygrowing and collapsing circular pattern.
 14. The method of imagingsubcutaneous blood vessels according to claim 12, further comprisingrepetitively driving said spot of light in a sequentially growing andcollapsing elliptical pattern.
 15. The method of imaging subcutaneousblood vessels according to claim 12, further comprising emitting saidbeam of light with said selective red wavelength being in the range of620 nm to 750 nm.
 16. A vein imager, for use in imaging subcutaneousveins beneath a target surface, said vein imager comprising: one laser,said one laser configured to emit a beam consisting of light at aselective red wavelength; a beam steering means configured to receivesaid beam of light from said one laser and to direct said beam onto thetarget surface to create a spot of light thereon, and to drive said spotof light to selectively move upon the target surface; means forinstantaneously measuring the amplitude of said selective red wavelengthof light reflected from said spot, throughout said selective movement; adrive circuit, said drive circuit configured to receive saidinstantaneous measurement of said reflected light amplitude from saidmeans for instantaneously measuring, and to determine a change in saidinstantaneous amplitude of reflected light throughout said selectivemovement; said drive circuit configured to cause an increase in anamount of power to said one laser when said drive circuit detects adecrease in said instantaneous amplitude; and said drive circuitconfigured to decrease the power to said one laser when said drivecircuit detects an increase in said instantaneous amplitude.
 17. Thevein imager according to claim 16, wherein said drive circuit furthercomprises a flagged amplitude, for use in eliminating a false indicationof no detected subcutaneous vein locations, wherein said flaggedamplitude is set to match said instantaneous measurement of saidreflected light amplitude of said spot, after said amount of power isincreased, and wherein said drive circuit is further configured todecrease said power to said one laser to occur when said drive circuitdetects said increase in said instantaneous amplitude, wherein saidincrease is relative to said flagged amplitude.
 18. The vein imageraccording to claim 16, wherein said selective movement of said spot uponthe target comprises movement in a pattern.
 19. The vein imageraccording to claim 16, wherein said beam steering means is configured torepetitively drive said spot of light in a sequentially growing andcollapsing pattern.
 20. The vein imager according to claim 19, whereinsaid beam steering means is configured to drive said spot of light insaid sequentially growing and collapsing pattern at a rate of at least30 Hz.
 21. The vein imager according to claim 20, wherein saidsequentially growing and collapsing pattern comprising a pattern fromthe group of patterns consisting of: an ellipse pattern; a circlepattern; and a spiral pattern.
 22. The vein imager according to claim16, wherein said selective red wavelength of light is in the range of620 nm to 750 nm.